Development of a mayenite composite pellet towards salinity remediation: Experimental demonstration of passive chloride removal from saline oilfield groundwater

This study investigates newly developed sand/gravel-sized mayenite composite pellets with cellulose-based binders as a chloride (Cl − ) remover that is compatible with saline groundwater also impacted by hydrocarbons. The mayenite pellets remove Cl − from impacted oilfield groundwater with 60–90 % efficiency in the range of salinity values found at field sites (< 20,000 mg/L total dissolved solids, TDS) in the presence of hydrocarbons, without agitation. The pellet reactions are driven by hydration, anion exchange, adsorption, and mineral phase reconstruction with increasing intraparticle diffusion and pellet heterogeneity during Cl − removal. Cl − removal is significantly correlated with changes in the quantities of pellet components. Mayenite is a key mineral for Cl − removal, during which hydrocalumite is formed. However, high mayenite purity is not required due to the contributions of non-mayenite pellet components (CaO and Al 2 O 3 ) to Cl − removal. Drastic morphological transformations of pellet minerals occurred from honeycomb-like to cubic or hexagonal structures. Sand/gravel-sized pellets had a comparable Langmuir q max of 74.5 mg/g. Mayenite pellets are not affected by hydrocarbons in both aqueous and nonaqueous phases. The removal of hydrocarbons observed was likely associated with porous pellet structures. TDS and competitive anions in impacted groundwater regulate the mayenite pellet reactions for Cl − removal. • Porous mayenite pellets were developed to remove Cl - from oilfield groundwater. • Mayenite pellets remove Cl - at various field salinities up to 20,000 mg/L TDS. • Rapid Cl - removal occurs via mineral reconstruction of multiple pellet components. • Impure mayenite pellets remove Cl - without mixing in the presence of hydrocarbons. • Mayenite pellets remove both Cl - and hydrocarbons from oilfield groundwater.